Lignin, the most abundant terrestrial biopolymer after cellulose, imparts structural integrity to the plant cell wall. While it is important for plant viability it impedes efficient use of woody biomass for biofuel production. Lignification increases the difficulty and energy costs of degrading the polysaccharide in the cell wall to simple fermentable sugars, thereby thwarting efficient ethanol production. Increased understanding of lignin biosynthesis and efficiently managing plant lignification will greatly facilitate the efficient generation of feedstocks for bioenergy and chemical, production.
The small molecule phenolic compounds that impinge upon or directly participate in lignin biosynthetic pathways also possess significant biological activities that are beneficial to humans. For example, their capacity to act as antioxidants is relevant to health issues such as cancer, cardiovascular and neurodegenerative diseases. These aromatic compounds are useful as flavorings in the food industry and are increasingly useful in cosmetic preparations, both as skin protectants as well as for their olfactory impacts.
Comparative structure-function analysis had revealed a detailed understanding of the basis for the regioselective O-methylation of lignin monomeric precursors and for other phenylpropanoids. A set of novel molecular tools, namely, modified (iso)eugenol-4-O-methyltransferases (m-IEMTs) (also called monolignol 4-O-methyltransferases or MOMTs) that may be effective for manipulation of lignin content and composition in plants have been generated. Particularly, m-IEMTs were created that specifically 4-O-methylate both the G- and the S-lignin precursors and modulate lignin content when expressed in transformed plants (Liu, et al., U.S. patent application publication US2012/117694A1, the entire contents of which are incorporated herein by reference).
In efforts to further develop 4-O-methyltransferases for lignin modification as well as for their potential to generate industrially useful chemicals and chemical feedstocks, specialized (iso)eugenol-4-O-methyltransferases (s-IEMTs) (which may also be identified herein as specialized monolignol-4-O-methyltransferases: s-MOMTs) that display specific preference for the G-lignin precursor p-coniferyl alcohol are provided. Some of the specialized (iso)eugenol-4-O-methyltransferases have enhanced activity for 4-O-methylation of ferulic acid and others for generation of iso-sinapyl alcohol from 5-hydroxyl coniferyl alcohol.